Crystalline silicoaluminophosphates having various pore structures have been proposed mainly by the researchers of Union Carbide Corporation (see, for example, Patent Document 1). Among others, SAPO-34 is recently attracting attention as a solid acid catalyst used for the synthesis, etc. of an olefin from a bio-alcohol that is a hydrocarbon resource substituting for petroleum.
However, when SAPO-34 is left in a water-containing atmosphere, its crystallinity decreases with time (see, for example, Non-Patent Document 1).
The crystalline silicoaluminophosphate decreases in its crystallinity with time when left in a water-containing atmosphere. In addition, the crystalline silicoaluminophosphate has a problem that the solid acidity is reduced as the crystallinity decreases due to hydration and unless special storage management blocked from the atmosphere is treated, SAPO-34 deteriorates during storage.
Other silicoaluminophosphates having a crystal structure different from that of SAPO-34 have been proposed as a solid acid catalyst for the synthesis of an olefin from an alcohol (see, for example, Patent Document 2).
These crystalline silicoaluminophosphates are characterized by the composition ((SixAlyPz)O2, wherein x: from 0.01 to 0.05, y and z: from 0.4 to 0.6) and the powder X-ray diffraction pattern. In addition, their associated silicoaluminophosphates have also been proposed (see, for example, Patent Document 3). These silicoaluminophosphates are characterized by the further different composition (SiO2/Al2O3 molar ratio: from 0.01 to 0.25) and the powder X-ray diffraction pattern.
However, all of these silicoaluminophosphates contain a very small amount of Si. A silicoaluminophosphate having a small Si amount has a problem that the amount of solid acid contained is small and when used for a solid acid catalyst, etc., the catalytic activity is low.
Recently, it has also been reported to use, as a catalyst, a novel silicoaluminophosphate composed of an intergrowth where a part of the CHA structure of SAPO-34 and a part of the AEI structure of SAPO-18 are complicatedly laminated (see, Patent Document 4). In this report, the intergrowth is proved to be a crystal different from SAPO-34 or SAPO-18 by X-ray crystal diffraction in combination with simulation results. Meanwhile, a crystal is specified by the ratio between AEI and CHA on the assumption, for descriptive purposes, that the crystal is a laminate of CHA structure and AEI structure, and specifically, a crystal having a CHA/AEI ratio of 90:10 is described.